Antarctic drilling peers deep into ice shelf’s past as open ocean

WELLINGTON – Scientists say they have drilled deeper than ever beneath the West Antarctic Ice Sheet, peering back millions of years to reveal signs it was once, at least in part, open ocean.

The vast expanse is estimated to hold enough ice to raise global sea levels by 4m to 5m, the international team of 29 researchers said.

By drilling through the ice and underlying sediment, they retrieved samples that reveal what it was like up to 23 million years ago.

The hope is that by studying how it melted in earth’s past, scientists can determine the factors that drove its retreat, including the ocean temperature at the time.

This could help predict how quickly the ice sheet may melt in a warming climate.

“Satellite observations over recent decades show the ice sheet is losing mass at an accelerating rate, but there is uncertainty around the temperature increase that could trigger rapid loss of ice,” they said in a report released on Feb 11 of their initial observations.

“Up until now, ice sheet modellers have relied on geological records from further afield,” they added.

They drilled through 523m of ice and 228m of ancient rock and mud at Crary Ice Rise on the Ross Ice Shelf.

‘Marine organisms’

“Some of the sediment was typical of deposits that occur under an ice sheet like we have at Crary Ice Rise today,” said co-chief scientist Molly Patterson of Binghamton University in the US.

They also found shell fragments and the remains of marine organisms that need light – material more typical of an open ocean, an ice shelf floating over water, or an ice-shelf margin with icebergs calving off, Dr Patterson said.

Scientists already thought the region was once open ocean, indicating a retreat of the Ross Ice Shelf and potential collapse of the West Antarctic Ice Sheet.

But there was uncertainty about when this happened.

The new record provided sequences of environmental conditions through time and direct evidence of the presence of open ocean in this region, Dr Patterson said.

Dr Huw Horgan, a co-chief of the project from Victoria University of Wellington, said initial indications show the samples span the past 23 million years.

This included periods when earth’s global average temperatures were significantly higher than 2 deg C above pre-industrial times, Dr Horgan said.

Drilling ended in January, and core samples have been transported from Crary Ice Rise, more than 1,100km across the Ross Ice Shelf to Scott Base, from where they will be sent to New Zealand for further analysis. AFP